A Philippine court entered a not guilty plea Monday for a U.S. Marine charged with murdering a transgender Filipino, allegedly after he discovered her gender when they checked into a hotel.

Marine Pfc. Joseph Scott Pemberton refused to enter a plea in the brief proceeding in a court in Olongapo city northwest of Manila, according to Justice Secretary Leila de Lima. Journalists were barred from the courtroom.

Dozens of left-wing protesters waved red flags outside the courthouse, demanding justice and an end to the U.S. military presence in the former American colony. Gay and lesbian groups have also staged protests denouncing the killing of Jennifer Laude, whose former name was Jeffrey, as a hate crime.

Monday's arraignment paves the way for Pemberton's trial, which lawyers of the victim's family said is scheduled to start next month.

"Finally justice can be attained for our sibling," Marilou Laude, the victim's sister, told reporters. She said she was shaking in anger when she saw the handcuffed suspect, who was guarded by several security escorts in the courtroom.

Pemberton has been charged by prosecutors in the Oct. 11 killing. They say the U.S. Marine strangled her and then drowned her in a hotel toilet after discovering she was a transgender woman. They had checked into the hotel after meeting in a bar.